Dr. Doom, the popular soubriquet of New York University economist Nouriel Roubini, who had recently turned more optimistic following years of prescient warnings on global economic trends, today warns of the rising risk of a double-dip W-shaped recession; ECB president, Jean-Claude Trichet warned at the week-end of more "difficult times" and meanwhile a study by two French economists, describes how money from European and Asian exporters ended up in US consumer or mortgage debt and how risk was transformed in the process. They argue that global imbalances would not have become so extreme if global finance had not provided exotic new instruments.